A randomized,double-blind, dose-finding,phase IIB study with Libertal has been performed in 493 volunteer smokers, wishing to quit. They were divided into 5 arms: 4 treatment groups of 0.5, 1.0, 2.0 and 4.0g/day respectively, and one placebo, divided BID. Treatment was administered during one week prior to smoking cessation, then continued during 8 weeks (56 days), followed by another 4 weeks without treatment (up to day 84). The primary endpoint was complete smoking cessation during at least 28 consecutive days. There were 6 on-site visits and 4 telephone interviews.